Shorting piston for wave guides



Sept. 30, 1947. E, G, UNDER 2,428,287

I SHORTING PISTON FOR WAVE GUIDES Filed May 18, 1943 I g v Z a 1, /7 U 4 6 2M9 1! /4 W 3nnentor Erna-fl lilz'rzder Gttbrneg particularly to a shorting Patented Sept. 30, 1947 Ernest G. Linder, Princeton,

Radio Corporation of America,

of Delaware Application May 18,

8 Claims.

This invention relates generally to super-high frequency transmission apparatus, and more piston for a conventional wave guide of rectangular cross-section.

Heretofore, various types of terminating pistons for wave guides have been employed to vary the effective length of resonant wave guide sections. However, all such slidable pistons have introduced serious power losses and extraneous wave reflections due to faulty electrical contact between the piston and the interior faces of the wave guide. The terminating piston carries considerable current in a wave guide transmission system in which any appreciable power is transmitted. It also is highly desirable that the shorting piston maintain substantially uniform orientation as it is adjusted longitudinally along the wave guide.

The instant invention effectively overcomes the various disadvantages of older devices mentioned heretofore, since the adjustable piston includes a novel spring contact arrangement which insures satisfactory contact between the piston and the adjacent interior walls of also provides satisfactory support for maintaining the piston face substantially normal to the axis of wave propagation.

The friction between the piston spring contact and the interior wave guide faces is also maintained at a practical value which permits smooth adjustment of the longitudinal position of the piston by means of a simple, externally located screw feed.

Among the objects of the invention is to provide an improved shorting piston for a superhigh frequency wave guide. Another object is to provide an improved shorting piston for a superhigh frequency wave guide of rectangular crosssection, wherein the longitudinal position of the piston within the guide may be adjusted by means of an externally located screw feed adjusting device. A further object of the invention is to provide an improved shorting piston for a rectangular wave guide super-high frequency transmission line, wherein the piston includes a novel spring contact device which insures good contact, smooth operation, and constant piston orientation within the guide. A further object of the invention is to provide an improved shorting piston for a super-high frequency wave guide, wherein the operative face of the piston is a concave surface substantially normal to the axis of wave propagation. An additional object is to provide an improved shorting piston and improved means for coupling a concentric trans- N. J., assignor to a corporation 1943, Serial No. 487,515

the wave guide, and

mission line to a super-high frequency wave guide, wherein the transmission line is coupled to the guide continuously adjacent a point of maximum current distribution, nothwithstanding longitudinal adjustment of th piston along the guide axis.

The invention will be described in further detail by reference to the accompanying drawing, of which Figure 1 is a cross-sectional view of a first embodiment of the invention, taken along the line I-I of Fig. 2; Figure 2 is a cross-sectional view of the same embodiment of the invention, taken along th line II-II of Fig. 1; and Figure 3 is a cross-sectional view of a second embodiment thereof. Similar reference numerals are applied to similar elements throughout the drawing.

Referring to the drawing, a wave guide I of rectangular cross-section is terminated by an apertured plug 2, which is secured in the end of the guide by means of screws 3. An adjustable shorting piston, disposed within the guide, includes a frame 4 substantially coextensive with the cross-sectional dimensions of the interior of the wave guide. The frame t includes a slotted portion 5 along two opposite faces thereof.

A U-shaped spring contact member 6 includes ends 1 formed .to fit within the slots '5, parallel faces adapted to provide sliding contact with two inside faces of the guide I, and a slightly concaved working face 9 substantially normal to the axis of wave propagation within the guide. Small screws in fasten the ends I of the U-shaped spring contact member to the piston frame 4 within the slots 5. Auxiliary pressure springs H are inserted under the parallel faces 8 of the contact spring 6, and anchored in suitable slots in the sides of the frame 4. These auxiliary pressure springs tend to expand the U-shaped contact spring to the shape of the inside surface of the guide, and insure satisfactory contact and smooth operation as th piston is moved longitudinally along the guide. Either, or both, the contact spring member 6 and the auxiliary pressure springs H may include longitudinal slots It or other means to facilitate conformation thereof to the inner wall of the guide.

An adjusting screw I2 is anchored to the piston frame 4 and extends through the aperture in the terminating plug 2 a predetermined distance outside of the end of the wave guide. A knurled adjusting nut l3, threaded to receive the adjusting screw it, includes a shoulder l4 which extends inside of the guide terminating plug 2. A pawl I5, attached to the inside surface of the terminating plug l2, engages the shoulder M to prevent 3 longitudinal movement of the adjusting nut I3. It will be seen that, as the adjusting nut 13 is rotated, the adjusting screw I 2, and hence the shorting piston, will be moved longitudinally along the interior of the wave guide.

Figure 3 is similar to Figures 1 and 2, with the exception that the adjusting screw I2 is hollow, and includes an insulated central coaxial conductor ll, which extends through an aperture I8 in the spring contact working face 9, and terminates in a coupling loop 19 which is connected to the end of the screw 12. The proportions of the coaxial conductors I2, I! may be selected to provide desired surge impedance, and the outer extremities thereof may be coupled in any conventional manner to an external line. It will be seen that the coupling loop [9 is coupled continuously to the wave guide I at a point of substantially maximum current distribution notwithstanding longitudinal adjustment of the shorting plug along the guide.

If desired, the longitudinal position of the shorting piston may be calibrated by including suitable indicia on the portion of the shorting screw 12 which projects through the adjusting nut l3.

Thus, the invention described comprises an improved shorting piston for a super-high froquency waveguide of rectangular cross-section, wherein substantially improved contact and piston adjustment are provided by means of a novel spring contact, and wherein an external line may be coupled eiiiciently to the guide at a point of maximum current distribution.

1 claim as my invention:

1. A shorting-piston for a super-high frequency wave guide comprising a, conductive frame substantially coextensive in cross-section with said guide, a spring contact member fastened to the sides of said frame adjacent the sides of said guide and shaped to present a concave surface substantially normal to the axis of wave propagation in said guide, and spring members fastened to said frame and disposed intermediate said frame and said contact member for increasing the pressure exerted by said contact member on said guide faces.

2. Apparatus of the type described in claim 1 including a lead screw fastened to said frame and extending longitudinally outside of said guide, and an adjusting member threaded to said screw for adjusting externally of said guide the longitudinal position of said piston therein.

3. A shorting-piston for a super-high frequency wave guide comprising a conductive frame substantially coextensive in cross-section with said guide, a spring contact member fastened to the sides of said frame adjacent the sides of said guide andshaped to present a concave surface substantially normal to the axis of wave propagation in said guide, and substantially flat spring members fastened to said frame and disposed intermediate said frame and said contact member for increasing the pressure exerted by said contact member on said guide faces.

4. Apparatus of the type described in claim 1 including a threaded apertured conductive wall terminating the end of said guide adjacent said shorting plug, and means operable through said apertured wall for adjusting the longitudinal position of said piston in said guide.

5. A shorting-piston for a super-high frequency wave guide comprising a conductive frame substantially coextensive in cross-section with said guide, a spring contact member fastened to the least portions thereof substantially normal to the axis of wave propagation in said guide, and subexerted by faces.

6. Apparatus of the type described in claim 1 characterized in that at least one of said spring and said spring contact members include longitudinal slots to facilitate conformation thereof to the inner surface of said guide.

7. Apparatus of the type described in claim 5 characterized in that at least one of said spring to the inner surface of said guide.

8. Apparatus of the type described in claim 1 including a hollow externally threaded cylindriing externally tion of said piston and said loop therein.

. ERNEST G. LINDER.

REFERENCES CITED The following references are of file of this patent:

UNITED STATES PATENTS record in the Number 

